1. Field of the Invention
The present invention relates to a display apparatus that performs color display using thin-film light-emitting devices.
2. Description of the Related Art
An organic electroluminescent device using electroluminescence of an organic material is configured by a light-emitting unit. The light-emitting unit is an accumulation of organic layers, e.g., positive hole transfer layer and light-emitting layer, between an anode and a cathode. Such an organic electroluminescent device has been receiving attention as a light-emitting device, which is capable of high-intensity light emission by low-voltage direct drive.
An exemplary full-color display apparatus using such an organic electroluminescent device has the configuration of including a color conversion layer for use with the organic electroluminescent device. The color conversion layer eliminates the need to form organic layers (light-emitting layers included) for each different color in the course of manufacturing the organic electroluminescent devices, i.e., the need for highly-precise coloring using a metal mask, so that the resulting display apparatus can perform full-color display.
In the display apparatus using such a color conversion layer, an organic electroluminescent device for color conversion is a blue light-emitting device, and subpixels of every color light are each provided with a blue light-emitting device. For subpixels of red and green lights, a color conversion layer is each provided on the light extraction side of the blue light-emitting devices. The color conversion layer serves to absorb the emitted blue lights, and use fluorescence or phosphor or combination thereof to make the absorbed blue lights glow in red or green. On the other hand, subpixels of blue lights are not provided with the color conversion layer, and the blue lights emitted from the blue light-emitting devices are to be extracted as they are. For more details, refer to Patent Document 1 (Patent Application Hei 5-258860).
In the organic electroluminescent devices (blue light-emitting devices) for use with a display apparatus using such a color conversion layer, either an anode or a cathode sandwiching therebetween a light-emitting layer is configured as a reflective electrode layer, and the remaining is configured as a light transmissive electrode layer. From the side of the light transmissive electrode layer, emitted lights are extracted. With such a configuration, the optical distance is optimized between the light-emitting layer and the reflective electrode layer to derive interference for emitted lights generated by the light-emitting layer of the blue light-emitting device, i.e., for interference and intensification between blue lights directly directing to the side of the light emissive electrode layer, and blue lights directing to the side of the light transmissive electrode layer after being reflected on the reflective electrode layer.
The issue with the display apparatus using such a color conversion layer is that, although the emitted blue lights are converted to the color of green with relatively high efficiency, the efficiency is not enough for conversion to the color of red. In consideration thereof, for the aim of increasing the efficiency for conversion to the color of red, proposed is the configuration of adding, to the blue light-emitting devices, a yellow light-emitting component having an absorption wavelength closer to that of the red conversion layer. Such component addition is claimed to increase the conversion efficiency for the red conversion layer, and the extraction intensity of the emitted red lights. For more details, refer to Non-Patent Document 1 (“Flat Panel Display 2004 (practice section)”, January 2003, P. 258), and Non-Patent Document 2 (“Flat Panel Display 2004 (strategy section)” January 2003, p. 194).